The art is replete with devices for removing solid or liquid particles from moving fluid (liquid or gas) streams ranging from filter paper and permeable solid members such as steel wool or glass wool, molybdenum fibers and ceramic fibers, to electroprecipitators, e.g., Cottrell precipitators. More recently with the growing concern over particulates in the air we breath, many developments have emerged. The present invention is principally concerned with removal of particles from exhaust gases from internal combustion and gas turbine engines.
Among the most visible offenders are diesel engines; automotive, marine, and stationary. Combustion is very often incomplete and disturbing black clouds of exhaust emanate from the exhaust stacks of such engines, particularly over-the-road trucks and buses. A considerable amount of effort has been expended to develop a satisfactory particulate trap for diesel engines. Reference may be had to commonly owned U.S. Pat. No. 4,725,411 of Richard C. Cornelison for one form of particulate trap for diesel engines.
The principal problem with prior art devices for trapping particulates has been in respect of regeneration of the trap for continued use. Use for a period of time causes the trap to become clogged with particulates, and unless the filter is to be replaced as a unit, as water filters usually are, the particulate trap or filter must undergo regeneration or flushing.
In the case of diesel exhaust particulate traps, regeneration or flushing is currently done by splitting the exhaust line at a "Y" and sending exhaust through one leg of the "Y" for particle removal, while the other leg of the "Y" is connected to a regenerating fluid, e.g., air and fuel at a temperature sufficient to "light off" the accumulated carbon. The exhaust stream is alternated between the regenerated side of the "Y" and the clogged side of the "Y" as required and then collected by a suitable header or inverted "Y" for passage out of the tail pipe.
The foregoing system is expensive and not entirely satisfactory because regeneration temperatures can reach 2400.degree. F. due to the exothermic potential of the carbon particles. The present invention solves this problem in an especially satisfactory way for the diesel engine.
Basically, it has been found that a very satisfactory particulate trap is provided by a rotary member rotating on an axis and disposed in intercepting relation with the flow of the exhaust gas. Generally, the diameter of the rotary member is greater than the diameter of the exhaust line in which it is inserted. A first segment of the "wheel" is open to the exhaust gas containing particulates, and a smaller second segment, isolated from the first segment, is adapted to receive a regenerating material, e.g., hot air or air and fuel. As the wheel rotates through the first segment, particles of carbonaceous material suspended in the exhaust are trapped by a specially configured member. As the wheel continues its rotation, it enters the isolated second segment and undergoes regeneration whereby the entrapped carbonaceous particles are burned off the trapping members and a fresh trapping section is again presented to the contaminated exhaust gases.
The trapping member is formed from catalyzed or non-catalyzed corrugated metal, with gauze, ceramics, or high temperature composites preferably in layers. In the case of layered materials several layers of such corrugated metal, or composites, are superimposed one on the other to build up a trapping segment or member. The layers are maintained in closely spaced relation. A convenient mode for spacing the layers is to apply a coating which tightly adheres to the surface and contains distributed therethrough temperature resistant particles of substantially uniform size, e.g., stainless steel particles, or particles of alumina, or zirconia particles. Alternatively, the particles may be applied to the wet surface and cemented thereto. Such particles are preferably spherical, although irregularly shaped particles of substantially uniform size may be used. Short wire segments may also be used as a spacing material.
The fluid traverses the trapping member in a direction substantially normal to the corrugations. The corrugations cause periodic rapid changes in the direction of the fluid and result in the particles dropping out of the fluid stream and being stored on the prepared surfaces of the trap material.